The present invention relates generally to the art of remote data acquisition and analysis devices, and more specifically to the art of remote data acquisition and analysis of pile driving operations. However, it will be appreciated that the system has wider application, such as in any situation in which real-time data acquisition and remote transmission is advantageously implemented.
Many of today's larger structures are fabricated with a foundation anchored to large piles that are driven into the soil. Since these piles form the dominant means of infrastructure support, it is crucial that they have known support characteristics. Such support characteristics are derived from analysis of physical characteristics obtained during the pile driving process. This process of real-time data acquisition and analysis is referred to as "dynamic pile testing."
Dynamic pile testing, such as that accomplished with the Pile Driving Analyzer.RTM., produced by the assignee of the subject invention ("PDA"), requires an impact pile driving hammer or a relatively small drop weight (typically 1 to 1.5% of test load). Usually several piles are tested in one day at a small fraction of the cost of a single static test. The PDA investigates driving stresses and integrity, hammer performance, and bearing capacity. The results from initial production piles or test programs are used to determine the pile installation criteria, for production quality control, or to solve problems experienced in the field, such as, when blow counts (set per blow) are unusually high or low, or when pile lengths are unexpectedly long or short. The PDA transmits such data to remote engineers who may quickly isolate the problem to hammer performance, pile defects, or soil condition.
Driving Stresses are usually the most extreme event in the life of a pile. The PDA measures the compressive stress near the pile top, evaluates bending and axial alignment, calculates the tension stress which is particularly important for concrete piles, and estimates the stress at the toe/bottom of the pile in hard driving situations. Knowing these driving stresses allows the installation procedure to be adjusted, if necessary, to keep stresses within accepted limits to reduce damage to the pile.
Continuous monitoring of the pile driving process affords significant advantages. Failure to diagnose changes in conditions or characteristics may result in loss or damage to piles or equipment and unnecessary effort or errors in creation of a foundation. The areas that merit continuous, real-time evaluation include:
Integrity Evaluation
If the pile driving characteristics of a pile are unusual, the possibility of pile damage exists. Real-time measurements are the most suitable mode for detection of early deflections caused by reduced pile stiffness from damage above the pile toe. PA1 Many pile foundation problems result from unanticipated hammer performance. Hammers delivering too much energy can damage the pile or drive the pile further than required for the established criteria, thereby increasing the costs of the foundation. Under-performing hammers increase installation time and cost, or cause the pile to refuse prematurely at high elevations resulting in failures from unacceptable settlements or low capacity. Since the hammer is also a quality control tool, routine and periodic data acquisition and testing verifies energy transfer to assure consistent performance and detect maintenance problems that may arise in larger products. Energy output of different hammers can be used to adjust the driving criteria and achieve uniform driving characteristics among all of the piles in a foundation. PA1 Together with the CAPWAP analysis the PDA is the only dynamic method available to reliably evaluate pile bearing capacity at the time of testing, as proven by extensive correlations. CAPWAP.RTM. is a rigorous analysis for determination of resistance distribution, dynamic response of the soil, and a simulated static load test evaluation. In sands, tests performed during driving can establish favorable pile lengths. For fine grained soils, testing during re-strike quantifies soil strength changes (set-up gains or relaxation losses); re-strike tests after sufficient wait periods of pile of different lengths can optimize pile lengths. PA1 Dynamic testing is frequently performed for bridges, wharfs, and other "near-shore" structures where static testing is difficult. PDA tests are easily adapted to drilled shafts and augured CFA piles, an application very common in Asia, Europe, and South America, and also provided in the USA by PDI's sister company (GRL and Associates) at great savings over other considered alternatives. Obviously, dynamic testing performed using the PDA are far less expensive than static testing or shaft replacement. PDA testing is also used extensively for pile monitoring of offshore oil platforms with both conventional and underwater hammers. PA1 Pile Integrity testing by low strain impacts with a hand-held hammer (also referred to as Sonic Pulse Echo test or Transient Response test); PA1 Parallel Seismic testing: a borehole is placed next to the pile; the pile is hit with a smaller hammer, the arrival time of the stress wave in the bore hole indicates the length of the pile; PA1 Cross Hole Sonic Logging: tubes are installed in the pile and stress waves generated in one tube are measured in a neighboring one; in this way concrete quality, horizontally between tubes is verified; PA1 Down Hole Sonic Logging: a single tube is used and wave emission and wave reception occurs in the same tube thus concrete quality in a vertical direction is verified; PA1 Non-destructive testing: utilizes small hammer impacts on many different structural elements.
Hammer Performance
Capacity
Other Applications
Dynamic testing can also take other forms using equipment similar to but not necessarily identical with the PDA. In all of these types of tests, whether they are performed on piles or other structural or geotechnical elements, the common denominator is the necessity to perform a test on a sit away from laboratory or office with relatively low level skills, while a highly educated and experienced engineer has to monitor and interpret the test in real time for reasons of test validity and economy. Such tests include:
While current pile driving data acquisition (PDA) devices are effective, they nonetheless require the presence of an engineer to be on site to view and draw conclusions from the resultant data. Many times construction sites are located in relatively inaccessible locations, or in countries where a scarce number of qualified engineers are available to monitor a large number of construction sites. Unavoidable construction delays or difficulties with scheduling of tests requires that engineers spend excessive and expensive time at the construction site.
The present invention addresses these and other drawbacks of earlier data acquisition devices, and provides a system by which pile driving data may be obtained, collected and communicated to a remote operator for real time or delayed analysis. The system provides for fault tolerance to accommodate the remote data acquisition and analysis. Given the fragile nature of data communication, such robustness is especially required in developing or third-world countries.